1. Field of the Invention
The present invention relates to a process for preparing an organic compound thin film for an optical device. Particularly, the thin film of the invention can be used in a non-linear optical device, photoelectric device, optical integrated-circuit device, and the like.
2. Description of the Prior Art
Organic compounds are attracting considerable attention in the above applicable fields thereof in that they have suitable characteristics but also allow relatively unrestrained material design. However, to use organic compounds in a practical device in such fields, molecules of these organic compounds need to be oriented and crystallized.
LB technique (Langmuir-Blodgett's technique) is conventionally known as a preparing technique of an organic thin film having an orientation property. This technique is characterized in that organic molecules, each of which has a hydrophilic group at one side and a hydrophobic group at the other side, are developed on a water surface so as to form a monomolecular layer, and such a layer is accumulated one after another with its molecules "stood" on a suitable substrate. Usually, this technique can yield a thin film whose molecular axis is oriented perpendicular to the substrate.
However, the following restrictions exist in LB technique to have a well-controllable and well-oriented monomolecular thin film. First, an organic molecule to be used must be so designed and synthesized as to have a long-chain alkyl group as a skeleton where a hydrophilic group and a hydrophobic group are well balanced at one end and the other end thereof, respectively. Second, since this technique is a wet method, materials to be used and applications of the film are restricted. In addition, since a monomolecular layer is stacked one after another, it takes long time to form a thin film.
There is a vacuum vapor deposition technique other than LB technique to have an organic compound thin film. This technique is a dry method and widely used to form an organic compound thin film of a low to high molecular compound.
Generally, it is not always easy to control orientation of molecules in this technique. To overcome this problem, Japanese Unexamined Patent Publication SHO 160427/1987 discloses such a technique that a polyester orientation film which is uniaxially oriented is used as a substrate to control orientation of vapor-deposited organic molecules. This technique is characterized in that a high molecular film as a substrate is rendered uniaxially oriented by drawing or the like, and an organic compound is vapor-deposited thereon by vacuum vapor deposition. However, a thin film prepared by the technique does not have enough orientation degree for practical use.
Thus, a thin film prepared by each of the above techniques does not have enough molecular orientation, therefore, it cannot exhibit enough non-linear optical effects such as a second harmonic and the like.